“30 Rock,” winner of three back-to-back comedy series Emmys, will air its centennial episode tonight in an installment involving Liz’s efforts to save “TGS With Tracy Jordan” from cancellation by bringing Jordan (Tracy Morgan) back.

“It’s not quite a cliffhanger,” Fey says. “There are exciting developments in Jack’s (Alec Baldwin) life, including the disappearance of his wife.”

photos/_specials_arts/30ROCK_(Tina-Fey-2011)150.jpg” vspace=”3″ hspace=”3″ align=”left”>”The hilarious, nonviolent disappearance,” Fey agrees. “The finale itself finds the staff returning to whatever their version of normal is. And it features an acting tour de force for Alec, who plays multiple characters in his own hallucination.”

Fey and Carlock took time from shooting the 100th to reflect on the evolution of their series and their relationship with their new bosses at cable provider Comcast, whom they mercilessly parody on the show as Kabletown.

“The biggest learning curve for me, coming from ‘Saturday Night Live,’ was to learn about story,” Fey says. “Story is not really a factor when you’re writing a sketch. Robert had that experience, having worked on ‘Friends’ and ‘Joey.’?”

Initially, the show focused more on behind-the-scenes antics at “TGS With Tracy Jordan.” Before the first season began, producers promised that full sketches hinted at on the show would be available online. That notion disappeared quickly because it was too time-consuming.

“We try really hard not to do sketches, because they’re so hard,” Carlock adds. “So we began to treat the show as a workplace comedy.”

Says Fey: “Pretty early on in season one, it became obvious that the relationship between Jack and Liz is the core of show, and we started building stories out from there.” Since then, she continues, “The show has gotten faster and faster. The speed can burn you out, but it wants to be fast.”

Carlock says the episode “Black Tie” (the 12th of season one) was where the staff learned where the show lay tonally. “We did make the network a little nervous on that one,” he admits. “We had to argue for that.”

In the episode, Paul Reubens played a prince riddled with physical and mental ailments due to “centuries of inbreeding” who cozied up to Jenna (Jane Krakowski). Jenna was conflicted: He repulsed her, but the idea of becoming royalty appealed to her. At a party in the prince’s honor, Jack encounters an ex (Isabella Rossellini) and introduces Liz to her as his girlfriend.

“To pull that off, we realized there had to be a balance in the sensibilities,” Carlock says. “The crazy stories must be handled in the most grounded fashion, while the most grounded stories can be handled more crazily. That was a learning experience for us on the show.”

Some of the most skewered shots from the past few years have been drawn from the real-life news of Comcast merging with NBC. The two insist their Kabletown jokes aren’t intended to draw blood.

“It was never our intention to see what we could get away with,” Fey says, who adds former parent company General Electric, rather than NBC, was the target of most of the show’s barbs.

“Hopefully, we’re far away from the reality of what’s really happening and not biting the hand that feeds us,” Carlock adds. “We’re never looking to stir the waters. Luckily, we have bosses with a good sense of humor.”

Both agreed that after 100 episodes, cranking out 22 half-hours of comic gold season after season hasn’t gotten any easier.

“We’re trying not to repeat ourselves, but I’m sure we do,” Carlock says. “Certain things are easier but others are even harder.”

Asks Fey, when looking at the totality of her work as both a writer and actress: “Why isn’t this getting easier?”